The present invention relates to a magnetic bead constructed in layers on a non-magnetic substrate for a recording medium which is provided with a magnetizable storage layer, into which information can be written along a track by vertical magnetization; which magnetic head comprises a conduction body similar to a ring head carrying the magnetic flux, having two magnet legs which consist of several magnetic layers of high-permeability material of predetermined saturation magnetization and of which the poles facing the recording medium are arranged at a predetermined spacing from each other, one behind the other as seen in the direction of motion of the head, and which delineate a space in between, through which the turns of an at least largely flat write/read coil winding extend. Such a magnetic head is shown, for instance, in DE-OS No. 29 24 013.
The principle of vertical magnetization for storing information is generally known (see, for instance, "IEEE Transactions on Magnetics," vol. MAG-16, no. 1, Jan. 1980, pages 71 to 76; EP No. 0 012 910 Al or the above mentioned DE-OS . For this principle, which is often also called perpendicular magnetization, special recording media in the form of rigid magnetic discs, individual flexible discs (floppy discs) or magnetic tapes are required Such a recording medium comprises at least one magnetizable storage layer of predetermined thickness which contains a magnetically anisotropic material, especially of a CoCr alloy. The axis of the so-called easy magnetization of this layer is oriented perpendicularly to the surface of the medium. By means of a special magnetic head the individual informations are then recorded along a track as bits in successive sections, also called cells or blocks, by appropriate magnetization of the storage layer. In practice, the magnetic flux changes, i.e., the transitions from one direction of magnetization to the opposite one, are generally used as information. The bits so obtained have a predetermined extent in the longitudinal direction of the track, also called the wavelength. This dimension can be substantially smaller than (horizontal) storage by demagnetization. Thereby, the information density in the recording medium can advantageously be increased by the principle of vertical magnetization.
However, the write and read heads known for the principle of longitudinal magnetization, i.e., heads by which the write as well as the read function can be executed, cannot be used directly also for vertical magnetization. While, if these heads are used, which generally are of ring head-like shape, the flux conduction desired also with the principle of vertical magnetization to form a circuit as closed as possible with low magnetic resistance can be achieved, it is difficult, with high bit densities and a correspondingly small gap width of the ring head, to generate a sufficiently strong writing field.
One is therefore compelled to develop for the principle of vertical magnetization, special write and read heads, the magnet legs of which are advantageously built up in layers of materials with high relative permeability u.sub.r in the order of 1000 or more and or relatively high saturation magnetization of generally more than 10 kA/cm. An embodiment of a corresponding magnetic head suitable therefor has in general conduction body carrying the magnetic flux with magnet leg which forms the so-called main pole, by which the sufficiently strong vertical magnetic field for changing the magnetization of the individual sections of the storage layer is produced. The necessary magnetic return can then be accomplished, for instance, by means of a so-called auxiliary pole, which is, for instance, located on the same side as the main pole and is formed by a further magnet leg (see, for instance "IEEE Trans. Magn.,"MAG-17, no. 6, Nov. 1982, pages 1158 to 1163; "J. Appl. Phys.," vol. 53, no. 3, 1982, pages 2593 to 2595, European Patent application No. 0 012 910 Al or DE-OS No. 29 24 013).
In this type of magnetic head with a shape of its conduction bodysimilar to a ring head, described for instance in the cited DE-OS, the auxiliary pole is to serve in any case only for the magnetic return of the flux. While a possible concurrent writing of this pole can optionally be tolerated if the recording main pole trails it and tberefore information written by the auxiliary pole can be overwritten, in order to largely suppress concurrent reading of the auxiliary pole with its trailing edge, the so-called air gap formed between the two poles would have to be relatively wide in order to ensure a far-reaching reduction of the magnetic flux density at the auxiliary pole. However, appropriately wide gap layers are difficult to realize in magnetic heads to be fabricated by a thin-film technique. In addition, the read signal attainable with magnetic heads of this type is generally relatively weak, since with this type the read as well as the write function must be executed by a single coil winding.
Because of these difficulties, magnetic heads have also been proposed in which the use of a separate auxiliary pole is dispensed with ("lEEE Trans. Magn.," vol. MAG-18, no. 6, November 1982, pages 1170 to 1172; European Patent application No. 0 071 489 A2). In this type of magnetic head only a single magnet leg facing the recording medium is provided with which, for instance, a planar write and read coil winding is associated. The necessary magnetic return is then accomplished by the stray flux. With such a magnetic head, also called a single-pole head, a field strength can be realized sufficient for recording with high bit densities for changing the magnetization of the storage layer and also a drop of the magnetic field at the trailing edge of the head as steep as possible is to be assumed such as for small transition widths of the magnetization reversal. (See, for instance, "IEEE Trans. Magn.," vol. MAG-19, no. 5, September 1983, pages 2239 to 2244). However, if the auxiliary pole is omitted, a sufficiently large read signal cannot be obtained with this head type.
Due to these mentioned problems in reading, systems are also known in which the function of writing and reading are executed by two separate heads. These heads can then be better adapted to the respective function (see for instance, "IEEE Trans. Magn.," vol. MAG-16, no. 5, September 1980, pages 967 to 972). Accordingly, ring heads known per se are used for reading, while writing can be carried out with the mentioned single-pole heads. A writing head suitable for this purpose has on its side facing the storage layer of the recording medium a main pole with a longitudinal dimension of, for instanc,, 3.mu.m, opposite which a substantially larger auxiliary pole is located on the back side of the recording medium. The second ring head required only for reading, on the other hand, has a gap width of, for instance, 0.2 .mu.m (see "IEEE Trans. Magn." vol. MAG-17, no. 6, November 1981, pages 2538 to 2540). Such systems for the magnetic reading and writing with special heads adapted to the respective function, however, are relatively elaborate as far as the mechanical design is concerned.